Full Idea
The customary morality, that which education and opinion have consecrated, is the only one which presents itself to the mind with the feeling of being in itself obligatory.
Gist of Idea
Orthodox morality is the only one which feels obligatory
Source
John Stuart Mill (Utilitarianism [1861], Ch.3)
Book Reference
Mill,John Stuart: 'Utilitarianism (including On Liberty etc)', ed/tr. Warnock,Mary [Fontana 1962], p.279